The moment you understand what dialogue can do in your screenplay, the better you become in writing good constructive dialogues

A story can be bad, the characters can be poorly created; but the dialogue alone can change the whole screenplay to good; the dialogue alone can strongly turn things around!
Dialogue is very powerful. It pulsates and releases the heart of the story. It speaks the mind of the writer, gives the reader a voice to read and then speaks for the script. Dialogue makes an audience speaks for the movie.

Just a line in the dialogue can connect the beginning of the screenplay with its end. One word in a dialogue can connect the 1st scene with the last scene. Just a phrase in a dialogue can take you deep into the heart of the story.

Dialogue brings back the past into the future.
Dialogue takes back the future into the past.
Dialogues bridges times differences.
Dialogue states the time, the setting, the actions and the characters in a particular scene